1. Field of the Invention
The present invention relates to an image classification apparatus and a recording medium having a program recorded therein.
2. Description of the Related Art
Image classification techniques have been used in various fields in recent years. For example, a technique of classifying which category out of two or more pre-defined categories an input image belongs to is used in optical character recognition (OCR), a facial recognition system (FRS). In these techniques, a category to which an input image belongs is classified through a step of extracting an area of a target to be classified, such as a character and a face, from the input image, a step of extracting feature value from the extracted area, and a step of comparing the extracted feature value with a feature value of each category prepared in advance, for example.
Further, for example, Japanese Laid-Open Patent Publication Nos. 8-180176 and 2006-163841 disclose techniques of classifying an image not based on the similarity of a specific target included in the image but based on the similarity of the overall composition of the image or an impression the image conveys. An image accumulating/managing apparatus of Japanese Laid-Open Patent Publication No. 8-180176 assigns an area number to each of the blocks obtained by dividing an image in a lattice manner, and uses an image index describing the attribute for each area, thereby being able to retrieve an image with high similarity as a whole. An image retrieval apparatus of Japanese Laid-Open Patent Publication No. 2006-163841 calculates total similarity using feature values, such as an aspect ratio, size, and barycentric coordinates, of each of partial areas constituting a document image, thereby retrieving the document image.
As such, an image whose overall composition is similar can be retrieved by acquiring the similarity between images, reflecting the similarity in shape and position between the areas, using feature value of each of the areas.
However, in natural phenomena, such as cell masses (cell colony) cultured by a cell culture apparatus and generation/growth of clouds, the shapes, sizes, directions, and positions of such targeted to be classified as cell masses and clouds vary and/or are unfixed. Thus, images belonging to the same category may be different from each other to a large degree in their overall compositions. Further, there is another case where it is difficult to accurately extract an area of the target to be classified since the outline of the target to be classified is unclear or a part of the target to be classified extends off a field of view of an image.
Thus, with the above described image classification techniques, it is impossible to classify a category with respect to an input image of a natural phenomenon, such as cell masses and clouds.